Target electrode for barrier grid storage tube



1965 c. L. DAY 3,201,628

TARGET ELECTRODE FOR BARRIER GRID STORAGE TUBE Original Filed June 28, 1957 [271/522 250?. Cy r'/'/ L. Day,

MKM

United States Patent 3,2l1,ii28 TARGET ELECTRODE FQR BAQRIER GRED STGRAGE THEE Cyril L. Day, Huntington, Ind, assignor to International Telephone and Telegraph Corporation Original application June 28, 1957, Ser. No. 668,671, now

Patent No. 3,023,622, dated Feb. 13, 13 62. Divided and this application Apr. 24, 1961, Ser. No. 194,959

1 Claim. (ill. 313-68) This invention relates to barrier grid storage tubes and more particularly to the target electrode assemblies incorporated in such tubes. This application is a division of my (to-pending application Serial Number 668,671, filed June 28, 1957, now Patent No. 3,020,622, issued February 13, 1962.

Barrier grid storage tubes are now commonly used in such devices as computers, being employed in binary computers for storing and reading-out yes-no" answers, and in a number of radar applications. These tubes, which are of the cathode ray type, are well-known in the art, as shown for example in Patent No. 2,538,836 of January 23, 1951, to A. S. Jensen. Such tubes conventially in clude an electron gun assembly including a cathode heated by a suitable filament, a control grid and an accelerating anode, positioned within an elongated envelope at one end thereof. Suitable deflecting and focusing elements are conventionally provided for causing the electron eam produced by the electron gun to scan a target electrode assembly positioned within the envelope at the other end thereof. The target electrode assembly comprises a grid or screen arranged on one side of the dielectric sheet and a metal plate arranged on the other.

The electron beam from the electron gun is caused to scan the target electrode assembly providing secondary emission greater than unity. Each square of the target electrode formed by the screen or grid in essence forms a separate capacitor with the metal backing plate and thus may be charged positively or negatively by the electron beam depending upon the polarity of the input signal applied to the metal plate and the screen of the target assembly. These charges may subsequently be taken oil of the target electrode assembly by a subsequent scanning by the electron beam.

In prior barrier grid storage tubes known to the applicant, the target electrode has been fiat. Barrier grid storage tubes having such fiat target electrodes have been restricted in resolution, i.e., the number of bits of infor mation stored for the diameter of the target, since it is essential that the electron beam impinge :on the target at nearly normal incidence; excessive shading results when the beam strikes the target at an angle substantially departing from the perpendicular. With a given flat target and a given diameter electron beam, it has in the past been possible to obtain only a given resolution and it has not been found possible appreciably to improve the resolution by increasing the diameter of the target since it becomes increasingly difiicult to collimate, i.e., focus, the beam. It is important, however, particularly in computers, that good resolution be provided in barrier grid storage tubes and further that there be a minimum of overlapping or cross-talk in reading-out bits of informa tion stored on the target. In order to decrease crosstalk, however, while retaining the same number of bits of information stored, i.e., the same resolution, or to increase the number of bits of information capable of storage by the target and thus increasing the resolution without increasing the cross-talk, it is necessary to increase the size of the target electrode or to decrease the size of the electron beam. However, as indicated above, the advantage to be gained by increasing the target diameter is diiiifizd Patented Aug. 1?, i365 limited as is the gain by decreasing the beam size. Furthermore, shading is introduced as the target diameter increases because the grid structure has appreciable thickness and thus there is a tendency in storage tubes having flat targets for the electron beam to be shaded by the thickness of the grid toward the edges of the target since the beam does not have normal incidence to the target except adjacent the center; any increase in the size of the target in an effort to decrease cross-talk or increase resolution by increasing the number of bits stored increases the shading effect adjacent the edges of the target. Furthermore, with fiat target electrodes, the beam is most accurately focused only at the center of the target and is increasingly oil focus as the outer edge of the target is approached; this also tends to increase cross-talk when the beam scans areas of the target adjacent the outer edges.

I have found that the above-mentioned disadvantages inherent in storage tubes having flat storage electrodes are substantially eliminated by providing a bowl-shaped or spherical target electrode preferably having the locus of its radius of curvature located approximately at the center of deflection of the electron beam. With such a bowl-shaped target electrode, the electron beam has normal incidence at all points on the target and thus the shading elfect encountered with ilat electrodes is eliminated; the beam is further properly focused at all points on the target rather than merely at the center, as in the case of fiat targets. Further, for a given diameter tube, the bowl-shaped target electrode provides more area and thus permits better resolution.

It is therefore an object of this invention to provide an improved target electrode for a barrier grid storage tube.

Another object of this invention is to provide a bowlshaped target electrode for a barrier grid storage tube.

A further object of this invention is to provide an improved barrier grid storage tube having a spherical shaped target electrode with its center of curvature located approximately at the center of deflection of the electron beam of the tube.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

In the drawings:

FIG. 1 is a schematic view of a barrier grid storage tube incorporating a conventional fiat target electrode;

FIG. 2 is a schematic view similar to FIG. 1 but illustrating a barrier grid storage tube incorporating my improved bowl-shaped target electrode; and

FIG. 3 is a view in cross-section of an actual barrier grid storage tube incorporating the improved target electrode of my invention.

Referring now to FIG. 1, there is shown in simplified form with non-essential details eliminated a prior art barrier grid storage tube 1 having an enclosing envelope 2 with a conventional electron gun assembly 3 located at end 4 of envelope 2 and with a conventional fiat target electrode assembly 5 located at the other end 6 of the envelope 2. For purposes of explanation, the components of the target electrode 5 have been disproportionately enlarged in FIG. I. The target electrode assembly 5 includes a metal backing plate 7 having a layer 8 of dielectric material arranged on the side thereof facing the electron gun assembly 3 and with a metal grid structure 9 arranged on the side of the dielectric layer 8 remote from the metal backing plate 7. The electron gun assembly 3 provides an electron beam ll which is caused to scan the target assembly 5 by means of deflecting elements 11, as is well known in the art.

I propriate sources of voltage.

It will be readily seen that the electron beam lil has a finite diameter and further that it does not have normal incidence to the target electrode assembly except at the center even if a collimating lens is used. Since the grid structure 9 has appreciable thickness, it is readily seen that the beam It will be shaded by the grid structure 9 adjacent the outer edges of the target 5, as clearly shown in FIG. 1. It is further seen that the resolution is restricted by the diameter of the beam in. It is also apparent that the beam 14) will be properly focused adjacent the center of the target electrode 5 only and will be increasingly out of focus as it approaches the outer edges due to geometrical and deflective defocusing.

Referring now to FIG. 2, in which like elements. are indicated by like reference numerals, it will be seen that I have provided a bowl-shaped target electrode 12, preferably spherical in configuration, with the locus of its radius of curvature R located approximately at the center of deflection 13 of beam 1%. Here it is seen that the metal I backing plate 14 is bowl-shaped with the dielectric layer 15 disposed on the inner surface of the bowl l4 and with the grid structure 16 similarly arranged on the side of the dielectric layer 15 remote from the metal backing plate 14. It will now be seen that the electron beam It has normal incidence with all points on the target electrode 12 and thus that shading previously encountered with fiat targets due to lack of normal incidence of the beam is eliminated. It will further be seen that with the diameter D of the envelope 2 of the tube of FIG. 2 the same as the diameter of the envelope 2 of the tube of FIG. 1, the target electrode being bowl-shaped in configuration will have a greater area than the fiat target electrode 5 of FIG. 1. Thus, it is possible to obtain better resolution. Conversely, any cross-talk encountered in the arrangement of PEG. 1 may be reduced by incorporating my improved bowl-shaped target electrode of FIG. 2, without reducing resolution. It is possible to increase the diameter of the curved target over that of a fiat target because it is now possible to assure normal incidence of the electron beam. It will also be readily apparent that the electron beam 1% will be properly focused at all points on the target electrode and not merely at the center as is the case of the flat target electrode of FIG. 1.

Referring now toFlG. 3, there is shown a barrier grid storage tube having an enclosing envelope 17 with a conventional electron gun assembly 18 positioned therein adjacent end 19. Electron gun assembly 18, which may include cathode, control grid, and accelerating elements, as is well known in the art, is provided with a plurality'of external leads 20 for connecting these elements'to ap- Vertical and horizontal deflection unit 21 is positioned'within envelope 17 in front of the electron gun assembly 18 and is adapted to be connected to suitable vertical and horizontal deflecting signals by leads 22 and 23; it will be readilyunderstood that external magnetic deflecting coils or conventional electrostatic plates may be employed for deflecting the electron beam 24 provided by the electron gun assembly 18 instead of the internal electrostatic deflecting unit 21 as shown in FIG. 3.

A shield electrode 25 is positioned within an envelope 28. Secondary emission accelerating electrodes 29 and 4-" adjacent the point of deflection 34 of the beam 24 and includes spherical metal backing plate 35 and spherical dielectric end grid elements generally identified as 36 disposed on the side of the metal backing plate 35 toward the electron gun assembly 18 for scanning by electron beam 24. The metal backing plate 35 of the target electrode 31 is adapted to be connected to a suitable source of voltage, such as plus or minus 50 (1-50) volts, by lead 37 and is also adapted to be connected to an output circuit, as is well-known in the art.

In an actual barrier grid storage tube constructed in accordance with FIG. 3, target electrode 31 had a diameter of 4 /2 inches and its radius of curvature was also 4 /2 inches. The dielectric layer was formed of glass .005 inch thick fused to the inner surface of the spherical metal backing plate 35, as described in my co-pending application Serial No. 666,969, filed June 20, 1957, and assigned to the assignee of the present application. The grid structure was a ZSO-mesh nickel screen .0015 inch thick. Such a screen could be fused to the surface of the dielectric layer remote from the metal backing plate 35 in the manner of my aforesaid application Serial No. 666,969.

In the method of making the improved target electrode of this invention, a blank of relatively thin metal is cut to proper size for forming the bowl. The bowl may be formed of suitable nonmagnetic metals such as copper, nickel, or stainless" steel; however, I have found that lnconel is preferred because of its good machining qualities, and further, since it is nonmagnetic and its expansion characteristics are approximately matched to the expansion characteristics of the glass dielectric layer. The blank is first degreased and then annealed in an inert atmosphere; I have annealed the blanks in dry hydrogen at 980? C. for twenty (20) minutes. The blank is then cooled, preferably with the dry hydrogen still flowing until the metal is returned to room temperature. In the event that metals other than Inconel are used, it is to be readily understood that annealing at a different temperature for a different period of time may be necessary in order to obtain the dead-soft anneal desired.

The annealed metal blanks are then drawn in a conventional die set to approximately the radius of curvature desired. The die set may'require some final shaping to obtain the correct curvature of the bowl since the springback in the mate-rial must be taken into consideration. After the bowl has been initially formed, it is again thoroughly degreased and returned to the furnace for another'annealing in an inert atmosphere. The blank is then annealed following the same schedule as the initial anneal and as soon as the annealing is completed, the bowl is replaced in the die set and restruck. The annealing and forming steps are continued until the bowl no longer changes its curvature during'annealing as determined by careful measurement with a spherorneter before and after annealing; I have found it necessary to repeat the annealing and forming cycle for from four to six times before the bowl becomes sufficiently stabilized.

After the bowl has been formed and stabilized, I have found it desirable to grind its interior surface utilizing conventional optical grinding equipment. I have carried on this grinding in two steps, first grinding with a fairly V coarse grit aluminum oxide, e.g., 180, until the bowl is I with other metals.

Following the grinding operation, the bowl is Washed,

care being take to insure that the ground inner surface is not scratched or the bowl deformed in any way. I have found that a soft bristle brush with a commercially available detergent washing powder is satisfactory for this cleaning step. Following washing with detergent, the bowl is finally rinsed in tape Water and then distilled water, the parts then being dried in an air oven at about 100 C.

A dielectric layer is then deposited on the inner surface of the bowl-shaped metal backing plate, preferably in accordance with the process described in my aforesaid application Serial No. 666,969, and a preformed fine mesh metal screen is positioned on to the surface of the dielectric layer, preferably in the manner described in my aforesaid application Serial No. 666,969.

It will now be readily apparent that I have provided an improved target electrode for a barrier grid storage tube, and an improved method of fabricating such a target electrode, this target electrode permitting greater resolution for the same tube diameter than that previously provided by fiat target electrodes, permitting the use of a larger diameter target than has been the case with flat targets, eliminating beam shading caused by the thickness of the grid structure, and providing more accurate reading-out by virtue of the proper focusing of the beam at all points on the target; my invention therefore results in a barrier grid storage tube having either better resolution or less cross-talk or both, features which are now highly desirable in computer technology.

While the preferred embodiment of this invention incorporates a glass dielectric layer fused to the bowlshaped metal backing plate and a bowl-shaped grid structure likewise fused to the glass dielectric layer as more fully described and illustrated in my aforesaid co-pending applications, it will be readily understood that other dielectric materials, such as aluminum oxide embedded in porcelain enamel, may be employed and that the grid structure may be mechanically held in assembled relation or secured to the dielectric layer by means of a suitable adhesive. It will further be understood that the barrier grid storage tube structure shown in the specific example of FIG. 3, aside from the bowl-shaped target electrode assembly, is shown for illustrative purposes only and that other well-known types of barrier grid storage tube construction may be equally advantageously employed.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

What is claimed is:

A barrier grid storage tube comprising: an envelope, an electron gun at one end arranged to produce an elecron beam; deflecting elements for deflecting said beam; 1 faceplate at one end; and an imperforate spherical target electrode spaced from said deflecting elements and adjacent said faceplate and arranged to be scanned by said beam, said target electrode having the locus of its radius of curvature located approximately at the center of deflection of said beam, said target electrode comprising a relatively thin spherical metal backing plate formed of a material maintaining a relatively stable curvature under diiferent temperature conditions and having a smoothly ground inner surface, a relatively thin layer of secondary electron emissive dielectric material on the inner surface of said backing plate; and a relatively thin fine wire mesh spherical metal electrostatic barrier grid in contact with the side of said dielectric layer remote from said backing plate and adapted to control the passage of electrons into and from said dielectric material.

References Cited by the Examiner UNITED STATES PATENTS 2,404,046 7/46 Flory et al. 1787.2 2,538,836 1/51 Jensen 31389 2,914,696 11/59 Eshbach 31389 X OTHER REFERENCES Cathode Ray Tube Displays, published by McGraW- Hill, 1948, pages 338 to 342 relied on.

JOHN W. HUCKERT, Primary Examiner.

RALPH G. NILSON, ARTHUR GAUSS, JAMES D.

KALLAM, Examiners. 

